The Deputy Prime Minister said that “people of very considerable personal wealth have got to make a bit of an extra contribution” towards what he describes as the “national effort”.

Mr Clegg will outline plans for his new wealth tax - which he suggests is necessary to ensure that British society remains “cohesive” - at the Liberal Democrats’ party conference next month.

The Coalition has already announced that the austerity programme of public spending cuts, including pay freezes in the public sector, will last for at least another two years until 2017. The deputy Prime Minister says today that this is only fair if accompanied by higher taxes on the wealthy.

The Liberal Democrat intervention, months before the budget, is likely to infuriate the Conservatives and spark a new round of Coalition infighting. It was described as a "dead end" by the Taxpayers' Alliance, which said it would "pose a huge danger to Britain's already struggling economy".

In an interview with The Guardian newspaper, the Liberal Democrat leader said: “If we are going to ask people for more sacrifices over a longer period of time, a longer period of belt tightening as a country, then we just have to make sure that people see it is being done as fairly and as progressively as possible.”

He added: “If we want to remain cohesive and prosperous as a society, people of very considerable personal wealth have got to make a bit of an extra contribution”.

One Tory MP, Bernard Jenkin, accused Mr Clegg of indulging in the "politics of envy", although Baroness Kramer, the Liberal Democrat Treasury spokesman in the Lords, insisted no one in society must be given a "free ride" from paying their fair share of tax.

Mr Jenkin claimed the plan was little more than a "clap line" to curry favour with activists at the Liberal Democrat party conference, a suggestion that seemed to be backed by the admission by Lady Kramer during a radio interview that she had no advance notice of the policy.

She told an interviewer on BBC Radio 4's Today programme: "I heard the plan for the first time just as you did, from Nick. It is going to be very interesting to hear the details."

The Liberal Democrats have long called for a so-called mansion tax on expensive properties worth more than £1m or £2m.

The Chancellor considered the mansion tax earlier this year, in return for Liberal Democrat support for scrapping the 50p higher rate of income tax, but rejected the plan.

However, in today’s interview, the deputy Prime Minister says that he is not seeking to restart the debate over a mansion tax but instead wants to introduce a new unspecified form of wealth tax.

It is unclear how such a tax, which would require a new system to be put in place to value people’s assets, could be put in place quickly.

Mr Clegg said: “In addition to our standing policy on things like the mansion tax is there a time limited contribution you can ask in some way or another from people of considerable wealth so they feel they are making a contribution to the national effort? What we are embarked on is, in some senses, a longer economic war rather than a short economic battle.”

He added: “What people once thought might have been a short sharp economic battle, a short sharp recession, is clearly turning into a longer term process of economic recovery and fiscal restraint. That begs big questions.”

Several other countries, including France, have targeted millionaires in their attempts to repair their public finances.

Earlier this year, Mr Clegg agreed to a deal which will see the top rate of income tax cut from 50 percent to 45 percent from next year in return of a crackdown on tax loopholes on the wealthy.

In the light of his comments, it was last night not clear how the Liberal Democrat leader can now continue to support the cut in the top rate without new taxes on the wealthy.

The wealth tax plan being floated is expected to dismay senior Conservatives and is likely to further sour relations between the Coalition partners. The Conservatives were upset that the Liberal Democrats sought to hold negotiations over the last budget in public and will not welcome a repeat of the situation starting so early in the process.

George Osborne, the Chancellor, is expected to reject calls for a new wealth tax amid fears it would deter international entrepreneurs.

Mr Clegg’s intervention comes just weeks before the Liberal Democrat conference at which the party leader is under pressure to show his credentials after abandoning House of Lords reform.

Last night, senior Conservative sources accused the deputy Prime Minister of “posturing”. They are braced for a far more tense relationship at the highest levels of government with more aggressive negotiations over wide areas of policy.

The Liberal Democrat leader says that “this is the time when we can start spreading our wings more”.

In the interview, Mr Clegg also signals that David Laws will return to Government in the forthcoming reshuffle.

“I have never made any secret of the fact that I want to see David Laws back in government,” he said. Mr Laws, who was forced to resign in May 2010 after being exposed for wrongly claiming expenses, is expected to be offered a position in the Cabinet Office.

Mr Clegg also calls for Ken Clarke, the Justice Secretary, not to be moved as David Cameron is considering.

He said that the Conservative Cabinet minister brings “earthy common sense” to the Government.

Matthew Sinclair, chief executive of the Taxpayers' Alliance, said Mr Clegg's wealth tax plan would be disastrous and a "practical nightmare to introduce". He said countries that had brought in similar levies had since abolished them after they proved unfair and led to "capital flight on an enormous scale".

He added: “With excessive taxes already choking off the economy and placing an excessive burden on families and businesses alike, the last thing the Coalition should be considering is new taxes. Politicians have spent too much, not taxed too little.”